BACKGROUND:
An ore is a mineral deposit which contains economically valuable minerals
that can be mined at a profit. Ores can contain metallic elements as well
as nonmetallic elements. Ores of metals include bauxite for aluminum,
hematite and magnetite for iron, galena for lead, cinnabar for
mercury,
pentlandite for nickel, cassiterite for tin, ilmenite for
titanium, and
wolframite for tungsten. Igneous, sedimentary, and metamorphic rocks can all
form ores.
After an ore is mined, the desirable minerals or elements must be
extracted from it. Extraction methods include crushing, sieving, density
separation, and magnetic separation. The result is a concentration of a
large quantity of the desired material. If the material is a metal, the
minerals are then melted and the metal can be retrieved through smelting.
Later, many smelted metals are mixed with other metals or nonmetals to form
alloys, which have different useful properties.
Metals have been very important in the evolution of the human society.
The malleability, strength, sharpness, and beauty of various metals allowed
early humans to fashion tools and jewelry. Prior to 3000 BC it was
discovered that copper could be produced by heating a certain type of bright
blue stone in a fire. This was the accidental beginning of smelting. Bronze,
composed of copper that has been melted and mixed with tin, became
widespread around 2000 BC. The resulting alloy was stronger than pure
copper, and could be sharpened, melted and recast into desirable shapes. By
750 BC, iron replaced bronze as the "metal of choice," thus
beginning the Iron Age.
PROCEDURE:
- Metallurgy is the science of metals. Have the students look at the
elements on the Periodic Placemat. They will notice that there are more
metals than any other type of element. Of the 90 naturally occurring
elements 70 are metals. In ores, many of these elements are found as
native elements: minerals composed of only one element.
- Use the placemats to point out the metallic elements. Give the
students examples of metal alloys:
steel is 98% iron and 2% carbon;
brass is 70% copper and 30% zinc;
bronze is 90% copper and 10% tin;
solder is 50% tin and 50% lead;
pewter is 91% tin, 7% antimony, and 2% copper;
stainless steel is 74% iron, 18% chromium, and 8% nickel; and
sterling silver is 93% silver, and 7% copper.
Make sure the students understand that these alloys are common and that
they see
them all the time. Make sure they know that they are metals derived from
ores enriched with minerals containing metallic elements.
- Students also see the term "cast" and "wrought"
iron in everyday life. These terms refer to different ways of working
with iron. Cast iron has a carbon content of 2-4%. Cast iron is poured
into a cast and hardened. Wrought iron on the other hand is shaped by
rolling, pressing, forging, or stamped at normal or elevated
temperatures. Wrought iron is stronger than cast iron.
- The Eyewitness book, Early Humans, explains the progression of
metals used in early society. You may want students to bring in
different examples of these metals. If you have Internet access you may
want students to search for "The Bronze Age," "The Iron
Age," and even the "Stone Age." to learn more about early
metalworking.
|
